This invention relates to a keypad, especially a keypad allowing entry of confidential information, such as the keypad of an Automated Teller Machine (ATM) into which a user enters a Personal Identity Number (PIN).
A known keypad may comprise a matrix of mechanical keys having on their undersides protrusions which apply pressure, when a key is operated, to a pressure-sensitive membrane, which is held by the keypad against a backing plate.
In an illegal attack on such a keypad, it is known for an attacker to remove the backing plate so as to insert a second pressure-sensitive membrane connected to an illegal recording means, or to tap the scan/return lines between the existing membrane and the other parts of the ATM. In either case, PINs can be deduced from captured data.
To detect such illegal removal of the securing plate, it is common to use one or more microswitches within the ATM casing which operate to provide a warning on removal of the backing plate.
Disadvantages of the use of microswitches are that:
a) Such switches are relatively bulky, and space to locate a switch in an ATM is restricted; PA1 b) There may be mechanical design problems related to mechanical tolerances and variations in switch activation points; PA1 c) Such switches are normally at positions where they are visible from outside the unit, or easily detectable by x-rays or other non-destructive means. Attackers are therefore able to disable or work around a microswitch alarm.